scholarly journals Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

2014 ◽  
Vol 14 (18) ◽  
pp. 25351-25410 ◽  
Author(s):  
P. Nabat ◽  
S. Somot ◽  
M. Mallet ◽  
M. Michou ◽  
F. Sevault ◽  
...  
Keyword(s):  
Land Surface ◽  
Radiative Forcing ◽  
Dust Aerosol ◽  
Dust Particles ◽  
Spatial And Temporal Variability ◽  
Surface Solar Radiation ◽  
Climate System Model ◽  
The Mediterranean ◽  
Daily Variability ◽  
Aerosol Radiative

Abstract. The present study investigates the effects of aerosols on the Mediterranean climate daily variability during summer 2012. Simulations have been carried out using the coupled regional climate system model CNRM-RCSM5 which includes prognostic aerosols, namely desert dust, sea salt, organic, black-carbon and sulfate particles, in addition to the atmosphere, land surface and ocean components. An evaluation of the dust aerosol scheme of CNRM-RCSM5 has been performed against in-situ and satellite measurements. This scheme shows its ability to reproduce the spatial and temporal variability of aerosol optical depth (AOD) over the Mediterranean region in summer 2012. Observations from the TRAQA/ChArMEx campaign also show that the model correctly represents dust vertical and size distributions. Thus CNRM-RCSM5 can be used for aerosol–climate studies over the Mediterranean. Here we focus on the effects of dust particles on surface temperature and radiation daily variability. Surface shortwave aerosol radiative forcing variability is found to be more than twice higher over regions affected by dust aerosols, when using a prognostic aerosol scheme instead of a monthly climatology. In this case downward surface solar radiation is also found to be better reproduced according to a comparison with several stations across the Mediterranean. Moreover, the radiative forcing due to the dust outbreaks also causes an extra cooling in land and sea surface temperatures. A composite study has been carried out for 14 stations across the Mediterranean to identify more precisely the differences between dusty days and the set of all the days. Observations show that dusty days receive less radiation at the surface and are warmer than average because of southwesterly fluxes often generating dust outbreaks. Only the simulation using the prognostic aerosol scheme is found to reproduce the observed intensity of the dimming and warming on dusty days. Otherwise, the dimming is underestimated and the warming overestimated.

scholarly journals Dust aerosol radiative effects during summer 2012 simulated with a coupled regional aerosol–atmosphere–ocean model over the Mediterranean

2015 ◽  
Vol 15 (6) ◽  
pp. 3303-3326 ◽  
Author(s):  
P. Nabat ◽  
S. Somot ◽  
M. Mallet ◽  
M. Michou ◽  
F. Sevault ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Mediterranean Region ◽  
Short Wave ◽  
Ocean Model ◽  
Dust Particles ◽  
Radiative Effects ◽  
Aerosol Radiative Forcing ◽  
Dust Aerosols ◽  
The Mediterranean ◽  
Aerosol Radiative

Abstract. The present study investigates the radiative effects of dust aerosols in the Mediterranean region during summer 2012 using a coupled regional aerosol–atmosphere–ocean model (CNRM-RCSM5). A prognostic aerosol scheme, including desert dust, sea salt, organic, black-carbon and sulphate particles, has been integrated to CNRM-RCSM5 in addition to the atmosphere, land surface and ocean components. An evaluation of this aerosol scheme of CNRM-RCSM5, and especially of the dust aerosols, has been performed against in situ and satellite measurements, showing its ability to reproduce the spatial and temporal variability of aerosol optical depth (AOD) over the Mediterranean region in summer 2012. The dust vertical and size distributions have also been evaluated against observations from the TRAQA/ChArMEx campaign. Three simulations have been carried out for summer 2012 with CNRM-RCSM5, including the full prognostic aerosol scheme, only monthly-averaged AOD means from the aerosol scheme or no aerosols at all, in order to focus on the radiative effects of dust particles and the role of the prognostic scheme. Surface short-wave aerosol radiative forcing variability is found to be more than twice as high over regions affected by dust aerosols, when using a prognostic aerosol scheme instead of monthly AOD means. In this case downward surface solar radiation is also found to be better reproduced according to a comparison with several stations across the Mediterranean. A composite study over 14 stations across the Mediterranean, designed to identify days with high dust AOD, also reveals the improvement of the representation of surface temperature brought by the use of the prognostic aerosol scheme. Indeed the surface receives less radiation during dusty days, but only the simulation using the prognostic aerosol scheme is found to reproduce the observed intensity of the dimming and warming on dusty days. Moreover, the radiation and temperature averages over summer 2012 are also modified by the use of prognostic aerosols, mainly because of the differences brought in short-wave aerosol radiative forcing variability. Therefore this first comparison over summer 2012 highlights the importance of the choice of the representation of aerosols in climate models.

scholarly journals Solar radiative forcing of aerosol particles near the Taklimakan desert during the Dust Aerosol Observation-Kashi campaign in Spring 2019

2020 ◽  
Author(s):  
Li Li ◽  
Zhengqiang Li ◽  
Wenyuan Chang ◽  
Yang Ou ◽  
Philippe Goloub ◽  
...  
Keyword(s):  
Land Surface ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Dust Aerosol ◽  
Dust Particles ◽  
Taklimakan Desert ◽  
Aerosol Radiative Forcing ◽  
Microphysical Properties ◽  
The Taklimakan Desert ◽  
Cooling Effects

Abstract. The Taklimakan desert is a main and continuous source of Asian dust particles causing a significant direct aerosol solar radiative forcing (ASRF). In order to improve the accuracy of the estimation of dust radiative forcing effects, the Dust Aerosol Observation-Kashi (DAO-K) campaign was carried out near the Taklimakan desert in April 2019. The objective of the campaign is to provide comprehensive parameters such as: dust optical and microphysical properties, vertical distribution and surface albedo, for the calculation of ASRF. The measurements were employed in radiative transfer (RT) simulations and the estimations are improved by considering the actual measured atmospheric profiles and diurnal variations of land surface albedo in addition to reliable aerosol parameters. The RT model estimates the ASRF results in average daily mean cooling effects of −19 W m−2 at the top of atmosphere and −36 W m−2 at the bottom of atmosphere during the DAO-K campaign. The Weather Research and Forecasting model with Chemistry (WRF-Chem) with assimilations of the aerosol optical depth and PM2.5 and PM10 concentrations measurements is prone to overestimate the radiative forcing effects of dust aerosols. The percent difference of daily mean ASRF between the two simulations are greater than 50 % in heavy dust episode. Ground-based observations of downward irradiances have validated that the RT simulations are in good agreement with simultaneous observations, whereas the WRF-Chem estimations exhibit obvious discrepancy with these independent measurements. Data assimilations can partly reduce the discrepancy, but there is still room for improving the WRF-Chem simulation of dust aerosol radiative forcing.

Comparison of radiative transfer schemes for the calculation of heating rates in the atmosphere of Mars

2021 ◽  
Author(s):  
Hao Chen-Chen ◽  
Santiago Pérez-Hoyos ◽  
Agustín Sánchez-Lavega
Keyword(s):  
Radiative Transfer ◽  
Radiative Forcing ◽  
Dust Aerosol ◽  
Dust Particles ◽  
Atmospheric Effects ◽  
Dynamical Models ◽  
Internal Radiation ◽  
Cooling Rates ◽  
Radiation Fields ◽  
Aerosol Radiative

<p><span>The ubiquitous dust aerosol particles in the atmosphere of Mars play a main role on the behaviour and evolution of its climate. By absorbing and scattering the incoming solar radiation, they modify the atmospheric thermal structure and dynamics. Dust radiative forcing calculations are of high relevance to understand Mars' overall atmospheric dynamics. The accuracy in determining internal radiation fields and the resulting atmospheric heating/cooling rates contribute to the uncertainties in these calculations.</span></p><p><span>Radiative transfer schemes using 2-stream approximations are widely implemented in multiple Mars’ dynamical models and Global Circulation Models (GCMs). The uncertainties associated to this approximation are related to neglecting details of dust particles’ scattering phase function: the higher the number of streams considered, the better the accuracy of the scheme, although there is a persistent trade-off between accuracy and computational cost. The objective of this work is to evaluate the accuracy of dust aerosol radiative forcing estimations in the Martian atmosphere by multiple-stream schemes.</span></p><p><span>Several scenarios covering the different atmospheric conditions during the Martian Year were simulated with different radiative transfer models, as well as other high-opacity dust storm scenarios. The atmosphere was discretised into 50 levels from 0 to 100 km, with atmospheric variables loaded from LMD’s Mars Climate Database (MCD). The visible and infrared spectral regions were divided into 12 bands, covering from 0.24 to 1,000 μm. Gaseous opacities were calculated with the correlated-k method, with absorption data retrieved from HITRAN. Dust aerosol radiative properties were derived using the wavelength-dependent properties reported by Wolff et al. (2006, 2009), with vertical distributions following a Conrath profile, and assuming a well-mixed dust scenario. Particle size (effective radius) and column dust opacity were given values to characterise every scenario. Finally, the calculated internal radiation fields and heating/cooling rates with the two-stream approximation code were compared with 4, 8, 16 and 32-stream solutions using the discrete ordinates method (DISORT).</span></p><p><span>The comparison of the results with respect to the 32-stream model shows heating rate underestimations with average differences of about 2.7, 0.3, 0.1, and 0.1 K/sol for the 2-, 4-, 8-, and 16-stream models, respectively. Such differences tend to be larger when there is more dust is loaded into the atmosphere. On the other hand, the average computational times for 1 sol using the 4-, 8-, 16-, and 32-stream schemes are about 15, 25, 40 and 135 times longer than the 2-stream scheme, respectively.</span></p><p><span>Future research prospects include the implementation of multiple-stream DISORT codes in Mars’ mesoscale dynamical models to investigate the accuracy of simulations of the atmospheric effects generated by local and regional dust storms.</span></p>

scholarly journals Impact of dust size parameterizations on aerosol burden and radiative forcing in RegCM4

2017 ◽  
Vol 17 (2) ◽  
pp. 769-791 ◽  
Author(s):  
Athanasios Tsikerdekis ◽  
Prodromos Zanis ◽  
Allison L. Steiner ◽  
Fabien Solmon ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Optical Depth ◽  
Radiative Forcing ◽  
Climate Model ◽  
Size Range ◽  
Regional Climate ◽  
Deposition Velocity ◽  
Research Unit ◽  
Dust Particles ◽  
Total Size ◽  
The Mediterranean

Abstract. We investigate the sensitivity of aerosol representation in the regional climate model RegCM4 for two dust parameterizations for the period 2007–2014 over the Sahara and the Mediterranean. We apply two discretization methods of the dust size distribution keeping the total mass constant: (1) the default RegCM4 4-bin approach, where the size range of each bin is calculated using an equal, logarithmic separation of the total size range of dust, using the diameter of dust particles, and (2) a newly implemented 12-bin approach with each bin defined according to an isogradient method where the size ranges are dependent on the dry deposition velocity of dust particles. Increasing the number of transported dust size bins theoretically improves the representation of the physical properties of dust particles within the same size bin. Thus, more size bins improve the simulation of atmospheric processes. The radiative effects of dust over the area are discussed and evaluated with the CALIPSO dust optical depth (DOD). This study is among the first studies evaluating the vertical profile of simulated dust with a pure dust product. Reanalysis winds from ERA-Interim and the total precipitation flux from the Climate Research Unit (CRU) observational gridded database are used to evaluate and explain the discrepancies between model and observations. The new dust binning approach increases the dust column burden by 4 and 3 % for fine and coarse particles, respectively, which increases DOD by 10 % over the desert and the Mediterranean. Consequently, negative shortwave radiative forcing (RF) is enhanced by more than 10 % at the top of the atmosphere and by 1 to 5 % on the surface. Positive longwave RF locally increases by more than 0.1 W m−2 in a large portion of the Sahara, the northern part of the Arabian Peninsula and the Middle East. The four-bin isolog method is to some extent numerically efficient, nevertheless our work highlights that the simplified representation of the four-bin approach produces less dust optical depth and RF, a fact that should be taken into account by future studies of the same region.

scholarly journals Modelled and observed changes in aerosols and surface solar radiation over Europe between 1960 and 2009

2015 ◽  
Vol 15 (16) ◽  
pp. 9477-9500 ◽  
Author(s):  
S. T. Turnock ◽  
D. V. Spracklen ◽  
K. S. Carslaw ◽  
G. W. Mann ◽  
M. T. Woodhouse ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Radiative Forcing ◽  
Climate Model ◽  
Suspended Particle ◽  
Sulfate Aerosol ◽  
Anthropogenic Aerosols ◽  
Surface Solar Radiation ◽  
Aerosol Mass ◽  
The Impact ◽  
Aerosol Radiative

Abstract. Substantial changes in anthropogenic aerosols and precursor gas emissions have occurred over recent decades due to the implementation of air pollution control legislation and economic growth. The response of atmospheric aerosols to these changes and the impact on climate are poorly constrained, particularly in studies using detailed aerosol chemistry–climate models. Here we compare the HadGEM3-UKCA (Hadley Centre Global Environment Model-United Kingdom Chemistry and Aerosols) coupled chemistry–climate model for the period 1960–2009 against extensive ground-based observations of sulfate aerosol mass (1978–2009), total suspended particle matter (SPM, 1978–1998), PM10 (1997–2009), aerosol optical depth (AOD, 2000–2009), aerosol size distributions (2008–2009) and surface solar radiation (SSR, 1960–2009) over Europe. The model underestimates observed sulfate aerosol mass (normalised mean bias factor (NMBF) = −0.4), SPM (NMBF = −0.9), PM10 (NMBF = −0.2), aerosol number concentrations (N30 NMBF = −0.85; N50 NMBF = −0.65; and N100 NMBF = −0.96) and AOD (NMBF = −0.01) but slightly overpredicts SSR (NMBF = 0.02). Trends in aerosol over the observational period are well simulated by the model, with observed (simulated) changes in sulfate of −68 % (−78 %), SPM of −42 % (−20 %), PM10 of −9 % (−8 %) and AOD of −11 % (−14 %). Discrepancies in the magnitude of simulated aerosol mass do not affect the ability of the model to reproduce the observed SSR trends. The positive change in observed European SSR (5 %) during 1990–2009 ("brightening") is better reproduced by the model when aerosol radiative effects (ARE) are included (3 %), compared to simulations where ARE are excluded (0.2 %). The simulated top-of-the-atmosphere aerosol radiative forcing over Europe under all-sky conditions increased by > 3.0 W m−2 during the period 1970–2009 in response to changes in anthropogenic emissions and aerosol concentrations.

scholarly journals Estimation of the aerosol radiative forcing at ground level, over land, and in cloudless atmosphere, from METEOSAT-7 observation: method and case study

2008 ◽  
Vol 8 (3) ◽  
pp. 625-636 ◽  
Author(s):  
T. Elias ◽  
J.-L. Roujean
Keyword(s):  
Optical Thickness ◽  
Temporal Variability ◽  
Radiative Forcing ◽  
Ground Level ◽  
Aerosol Optical Thickness ◽  
Reference Level ◽  
Urban Site ◽  
Spatial And Temporal Variability ◽  
Aerosol Radiative Forcing ◽  
Aerosol Radiative

Abstract. A new method is proposed to estimate the spatial and temporal variability of the solar radiative flux reaching the surface over land (DSSF), as well as the Aerosol Radiative Forcing (ARF), in cloud-free atmosphere. The objective of regional applications of the method is attainable by using the visible broadband of METEOSAT-7 satellite instrument which scans Europe and Africa on a half-hourly basis. The method relies on a selection of best correspondence between METEOSAT-7 radiance and radiative transfer computations. The validation of DSSF is performed comparing retrievals with ground-based measurements acquired in two contrasted environments: an urban site near Paris and a continental background site located South East of France. The study is concentrated on aerosol episodes occurring around the 2003 summer heat wave, providing 42 cases of comparison for variable solar zenith angle (from 59° to 69°), variable aerosol type (biomass burning emissions and urban pollution), and variable aerosol optical thickness (a factor 6 in magnitude). The method reproduces measurements of DSSF within an accuracy assessment of 20 W m−2 (5% in relative) in 70% of the situations, and within 40 W m−2 in 90% of the situations, for the two case studies considered here. Considering aerosol is the main contributor in changing the measured radiance at the top of the atmosphere, DSSF temporal variability is assumed to be caused only by aerosols, and consequently ARF at ground level and over land is also retrieved: ARF is computed as the difference between DSSF and a parameterised aerosol-free reference level. Retrievals are linearly correlated with the ground-based measurements of the aerosol optical thickness (AOT): sensitivity is included between 120 and 160 W m−2 per unity of AOT at 440 nm. AOT being an instantaneous measure indicative of the aerosol columnar amount, we prove the feasibility to infer instantaneous aerosol radiative impact at the ground level over land with METEOSAT-7 visible channel.

Evaluating the Influence of Plant-Specific Physiological Parameterizations on the Partitioning of Land Surface Energy Fluxes

2015 ◽  
Vol 16 (2) ◽  
pp. 517-533 ◽  
Author(s):  
Mauro Sulis ◽  
Matthias Langensiepen ◽  
Prabhakar Shrestha ◽  
Anke Schickling ◽  
Clemens Simmer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Latent Heat ◽  
Land Surface ◽  
Radiative Forcing ◽  
Carbon Fixation ◽  
Gross Primary Production ◽  
Heat Fluxes ◽  
Physiological Characteristics ◽  
Spatial And Temporal Variability ◽  
Physiological Properties

Abstract Plant physiological properties have a significant influence on the partitioning of radiative forcing, the spatial and temporal variability of soil water and soil temperature dynamics, and the rate of carbon fixation. Because of the direct impact on latent heat fluxes, these properties may also influence weather-generating processes, such as the evolution of the atmospheric boundary layer (ABL). In this work, crop-specific physiological characteristics, retrieved from detailed field measurements, are included in the biophysical parameterization of the Terrestrial Systems Modeling Platform (TerrSysMP). The physiological parameters for two typical European midlatitudinal crops (sugar beet and winter wheat) are validated using eddy covariance fluxes over multiple years from three measurement sites located in the North Rhine–Westphalia region of Germany. Comparison with observations and a simulation utilizing the generic crop type shows clear improvements when using the crop-specific physiological characteristics of the plant. In particular, the increase of latent heat fluxes in conjunction with decreased sensible heat fluxes as simulated by the two crops leads to an improved quantification of the diurnal energy partitioning. An independent analysis carried out using estimates of gross primary production reveals that the better agreement between observed and simulated latent heat adopting the plant-specific physiological properties largely stems from an improved simulation of the photosynthesis process. Finally, to evaluate the effects of the crop-specific parameterizations on the ABL dynamics, a series of semi-idealized land–atmosphere coupled simulations is performed by hypothesizing three cropland configurations. These numerical experiments reveal different heat and moisture budgets of the ABL using the crop-specific physiological properties, which clearly impacts the evolution of the boundary layer.

scholarly journals The climatology of dust aerosol over the arabian peninsula

2015 ◽  
Vol 15 (2) ◽  
pp. 1523-1571 ◽  
Author(s):  
A. Shalaby ◽  
B. Rappenglueck ◽  
E. A. B. Eltahir
Keyword(s):  
Land Surface ◽  
Radiative Forcing ◽  
Large Scale ◽  
Surface Albedo ◽  
Arabian Peninsula ◽  
Mineral Dust ◽  
Dust Storms ◽  
Dust Aerosol ◽  
Dust Aerosols ◽  
Mineral Dust Aerosols

Abstract. Dust storms are considered to be a natural hazard over the Arabian Peninsula, since they occur all year round with maximum intensity and frequency in Spring and Summer. The Regional Climate Model version 4 (RegCM4) has been used to study the climatology of atmospheric dust over the Arabian Peninsula from 1999 to 2012. This relatively long simulation period samples the meteorological conditions that determine the climatology of mineral dust aerosols over the Arabian Peninsula. The modeled Aerosol Optical Depth (AOD) has been compared against ground-based observations of three Aerosol Robotic Network (AERONET) stations that are distributed over the Arabian Peninsula and daily space based observations from the Multi-angle Imaging SpectroRadiometer (MISR), the Moderate resolution Imaging SpectroRadimeter (MODIS) and Ozone Monitoring Instrument (OMI). The large scale atmospheric circulation and the land surface response that lead to dust uplifting have been analyzed. While the modeled AOD shows that the dust season extends from March to August with two pronounced maxima, one over the northern Arabian Peninsula in March with AOD equal to 0.4 and one over the southern Arabian Peninsula in July with AOD equal to 0.7, the observations show that the dust season extends from April to August with two pronounced maxima, one over the northern Arabian Peninsula in April with AOD equal to 0.5 and one over the southern Arabian Peninsula in July with AOD equal to 0.5. In spring a high pressure dominates the Arabian Peninsula and is responsible for advecting dust from southern and western part of the Arabian Peninsula to northern and eastern part of the Peninsula. Also, fast developed cyclones in northern Arabian Peninsula are responsible for producing strong dust storms over Iraq and Kuwait. However, in summer the main driver of the surface dust emission is the strong northerly wind ("Shamal") that transport dust from the northern Arabian Peninsula toward south parallel to the Arabian Gulf. The AERONET shortwave Top of Atmosphere Radiative Forcing (TOARF) and at the Bottom of Atmosphere Radiative Forcing (BOARF) have been analyzed and compared with the modeled direct radiative forcing of mineral dust aerosol. The annual modeled TOARF and BOARF are −3.3 and −12 W m−2, respectively. However, the annual observed TOARF and BOARF are significantly different at −10 and −52 W m−2, respectively. The analysis of observed and modeled TOARF agrees with previous studies in highlighting the need for more accurate specification of surface albedo over the region. Due to the high surface albedo of the central Arabian Peninsula, mineral dust aerosols tend to warm the atmosphere in summer (June–August).

scholarly journals Modelled and observed changes in aerosols and surface solar radiation over Europe between 1960 and 2009

2015 ◽  
Vol 15 (9) ◽  
pp. 13457-13513 ◽  
Author(s):  
S. T. Turnock ◽  
D. V. Spracklen ◽  
K. S. Carslaw ◽  
G. W. Mann ◽  
M. T. Woodhouse ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Sulfate Aerosol ◽  
Anthropogenic Aerosols ◽  
Surface Solar Radiation ◽  
Aerosol Mass ◽  
The Impact ◽  
Aerosol Radiative

Abstract. Substantial changes in anthropogenic aerosols and precursor gas emissions have occurred over recent decades due to the implementation of air pollution control legislation and economic growth. The response of atmospheric aerosols to these changes and the impact on climate are poorly constrained, particularly in studies using detailed aerosol chemistry climate models. Here we compare the HadGEM3-UKCA coupled chemistry-climate model for the period 1960 to 2009 against extensive ground based observations of sulfate aerosol mass (1978–2009), total suspended particle matter (SPM, 1978–1998), PM10 (1997–2009), aerosol optical depth (AOD, 2000–2009) and surface solar radiation (SSR, 1960–2009) over Europe. The model underestimates observed sulfate aerosol mass (normalised mean bias factor (NMBF) = −0.4), SPM (NMBF = −0.9), PM10 (NMBF = −0.2) and aerosol optical depth (AOD, NMBF = −0.01) but slightly overpredicts SSR (NMBF = 0.02). Trends in aerosol over the observational period are well simulated by the model, with observed (simulated) changes in sulfate of −68% (−78%), SPM of −42% (−20%), PM10 of −9% (−8%) and AOD of −11% (−14%). Discrepancies in the magnitude of simulated aerosol mass do not affect the ability of the model to reproduce the observed SSR trends. The positive change in observed European SSR (5%) during 1990–2009 ("brightening") is better reproduced by the model when aerosol radiative effects (ARE) are included (3%), compared to simulations where ARE are excluded (0.2%). The simulated top-of-the-atmosphere aerosol radiative forcing over Europe under all-sky conditions increased by 3 W m−2 during the period 1970–2009 in response to changes in anthropogenic emissions and aerosol concentrations.

scholarly journals The Sensitivity of Simulated River Discharge to Land Surface Representation and Meteorological Forcings

2010 ◽  
Vol 11 (2) ◽  
pp. 334-351 ◽  
Author(s):  
Stefano Materia ◽  
Paul A. Dirmeyer ◽  
Zhichang Guo ◽  
Andrea Alessandri ◽  
Antonio Navarra
Keyword(s):  
Land Surface ◽  
Radiative Forcing ◽  
River Discharge ◽  
General Circulation ◽  
Global Climate ◽  
The United States ◽  
Climate Simulation ◽  
Good Representation ◽  
Eastern Asia ◽  
The Mediterranean

Abstract The discharge of freshwater into oceans represents a fundamental process in the global climate system, and this flux is taken into account in simulations with general circulation models (GCMs). Moreover, the availability of realistic river routing schemes is a powerful instrument to assess the validity of land surface components, which have been recognized to be crucial for the global climate simulation. In this study, surface and subsurface runoff generated by the 13 land surface schemes (LSSs) participating in the Second Global Soil Wetness Project (GSWP-2) are used as input fields for the Hydrology Discharge (HD) routing model to simulate discharge for 30 of the world’s largest rivers. The simplest land surface models do not provide a good representation of runoff, and routed river flows using these inputs are affected by many biases. On the other hand, HD shows the best simulations when forced by two of the more sophisticated schemes. The multimodel ensemble GSWP-2 generates the best phasing of the annual cycle as well as a good representation of absolute values, although the ensemble mean tends to smooth the peaks. Finally, the intermodel comparison shows the limits and deficiencies of a velocity-constant routing model such as HD, particularly in the phase of mean annual discharge. The second part of the study assesses the sensitivity of river discharge to the variation of external meteorological forcing. The Center for Ocean–Land–Atmosphere Studies version of the SSiB model is constrained with different meteorological fields and the resulting runoff is used as input for HD. River flow is most sensitive to precipitation variability, but changes in radiative forcing affect discharge as well, presumably because of the interaction with evaporation. Also, this analysis provides an estimate of the sensitivity of river discharge to precipitation variations. A few areas (e.g., central and eastern Asia, the Mediterranean, and much of the United States) show a magnified response of river discharge to a given percentage change in precipitation. Hence, an amplified effect of droughts as indicated by the consensus of climate change predictions may occur in places such as the Mediterranean. Conversely, increasing summer precipitation foreseen in places like southern and eastern Asia may amplify floods in these poor and heavily populated regions. Globally, a 1% fluctuation in precipitation forcing results in an average 2.3% change in discharge. These results can be used for the definition and assessment of new strategies for land use and water management in the near future.

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